1. Field of the Invention
This invention relates to pressure control devices for fluids and more particularly relates to devices for maintaining a selected pressure in air compressing systems and specifically relates to such pressure-maintaining devices in refrigeration and air conditioning systems in which air is the working medium.
2. Review of the Prior Art
There are many fields in which a selected pressure must be maintained by a regulating device. For example, U.S. Pat. No. 3,604,452 describes a device for regulating the flow of natural gas from a supply line; U.S. Pat. No. 3,083,546 describes a two-fluid system employing a pair of opposing diaphragms of unequal area in an aircraft anti-ice control system; and U.S. Pat. No. 3,974,752 teaches a combination of a pair of springs and a pair of opposed diaphragms of unequal areas which are acted upon by aircraft cabin pressure and by comparative pressure within a memory chamber.
None of these devices, however, combines a comparison means with a pressure-relieving means and a pressure-increasing means that operates to regulate pressure within a system without dumping fluid therefrom while admitting additional fluid.
Such a pressure-control device is especially needed for a rotary-vane air cycle system for air-conditioning automobiles and either cooling a building as an air conditioner or heating a building as a heat pump. In such a device, air as the working fluid is compressed in a rotary-vane air compressor to a pressure of one to nine atmospheres and a temperature of 150.degree.-200.degree. F. or more, cooled in a heat exchanger to a temperature of about 10.degree. F. above ambient, re-introduced into the compressor, expanded therein to a much lower temperature, and heat exchanged or otherwise used for air conditioning and cooling purposes.
A rotary-vane air compressor that has been described in popular literature is disclosed in the following U.S. Pat. Nos. 3,686,893; 3,877,245; 3,884,664; 3,886,763; 3,886,764; 3,886,765; 3,904,327; 3,956,904; 3,967,466; 3,968,649; 3,974,752; and 3,977,852. This device and its utility was described, for example, in "Sensational New Auto Air Conditioner: It Cools Without Refrigerant," by E. F. Lindsey, Popular Science, 54, December 1970, pages 54 and 55, and in "Rovac -- Now It Can Heat and Cool Your House," by E. F. Lindsey, Popular Science, August 1976, 84-87, 119.
Control of the pressure entering such a rotary-vane air compressor is a very satisfactory way to control the expander exit temperature and the system capacity, but achieving such control to the degree of precision that is needed is not a simple matter. Satisfactory control devices do exist for large air conditioning and compressing systems in which air is the working fluid, such as the cabins of large aircraft. Smaller units having the compactness, economy of manufacture, precision of control, long working life, and sensitive response characteristics that are needed for air conditioning purposes, especially in automobiles, are not to be found at the present time.